The invention relates generally to electromagnetic compatibility, and more specifically to an air duct designed to reduce electromagnetic radiation.
Modern electronic devices that rely upon computerized circuits or digital logic typically conduct voltage signals within the circuits that change at very fast rates. Because digital logic is usually implemented in terms of ones and zeros, with ones being represented by some positive voltage such as 5 v or 3.3 v, and zeros being represented by zero voltage, such circuits must quickly change state from a positive voltage to zero voltage millions or billions of times per second to provide the capability to quickly calculate or process information.
These rapid changes in voltage state within such circuits can be viewed over time as approximating what is known as a square wave, wherein the voltage changes between states almost instantaneously. In practice, all circuits have limited bandwidth, and so a perfect square wave is not achieved. But, the approximate square wave that appears in most digital logic circuits changes state more quickly with faster circuits and switching times, and contains higher frequency components as it changes state more quickly.
These high frequency components can be easily radiated from a computerized device as electromagnetic fields from the electronic circuit, especially when the wavelength of the high frequency components is short enough to become a significant fraction of the conductive traces or wires that connect the circuit components to each other, which then become effective antennas. Digital signals are rich in spectral content, often containing significant energy over a wide bandwidth of the radio spectrum. These signals must be shielded to reduce emissions to certain levels before a digital electronic product can be sold according to requirements imposed by most countries, and so must be understood and controlled in the design process.
Unfortunately, modern computational devices also typically produce significant amounts of heat, and must be cooled. This is typically achieved by forced air ventilation, which requires that a physical hole exist between the digital circuitry and the outside air. Such a hole can allow electromagnetic radiation to escape in addition to the intended consequence of venting heat, and can become a serious design problem when electromagnetic emissions must be controlled.
What is desired is a system and method for reducing the electromagnetic emissions radiated from a digital electronic device through air ducts or passages.
The present invention provides an air duct for ventilating an electronic device having a processor. The air duct comprises one or more walls that have an irregular surface and that further have a layer of conductive material applied to the irregular surface. Further embodiments of the invention include electronic device enclosures and electronic devices having an air duct featuring an irregular interior surface and having conductive material applied to the irregular surface.